mutations

The definitions used in this glossary of terminology either have been
provided by the authors of the articles, or have been extracted wholly or in
part, or paraphrased from the following sources: The American Medical
Association Encyclopedia of Medicine, Charles B. Clayman, MD, Medical
Editor, Random House, New York, 1989; Biotechnology from A to Z, 2d
Edition, William Bains, Oxford University Press, New York, New York, 2002;
A Dictionary of Genetics, 6th Edition, Robert C. King and William D.
Stansfield, Oxford University Press, New York, New York, 2002; Dorland's
Illustrated Medical Dictionary, 29th and 30th Editions, W. B. Saunders
Company, Philadelphia, 2000, 2003; Genes VII, Benjamin Lewin, Oxford
University Press, New York, New York, 2000; The Gale Encyclopedia of
Genetic Disorders, Volumes I and II, Stacey L. Blachford, Ed., Thomson
Learning, New York, New York, 2002; The Merriam-Webster Dictionary,
Merriam-Webster, Inc., Springfield, Massachusetts, 1997; Molecular
Biology of the Cell, 3rd Edition, Bruce Alberts, et al., Garland
Publishing, 1994; The Random House Dictionary of the English
Language, Unabridged Edition, 1966; Webster's Ninth New Collegiate
Dictionary, 1991.

quality

DEFINITION:

1. Peculiar and essential character; nature. 2. Degree of excellence.3. A distinguishing attribute.4. In radiology, the ability of a particular form or type of ionizing radiation to penetrate matter.

genetics

DEFINITION:

The study of genes and their heredity.

gene

DEFINITION:

A segment of a DNA molecule that contains all the information required for synthesis of a product (polypeptide chain or RNA molecule), including both coding and non-coding sequences. It is the biological unit of heredity, self-reproducing, and transmitted from parent to progeny. Each gene has a specific position (locus) on the chromosome map. From the standpoint of function, genes are conceived of as structural, operator, and regulatory genes.

wild-type gene - The normal allele of a gene, sometimes symbolized by +.

X-linked gene - A gene carried on the X chromosome; the corresponding trait, whether dominant or recessive, is always expressed in males, who have only one X chromosome. X linkage is used sometimes synonymously with sex linkage since no genetic disorders have as yet been associated with genes on the Y chromosome.

mutation

DEFINITION:

frameshift mutation - A mutation resulting from an addition or subtraction that is not an exact multiple of 3 base pairs in a coding sequence. From the point of mutation onwards, base triplets (codons) are read out of phase; the reading frame of the gene is changed, and a completely different set of amino acids is made into protein.

loss-of-function mutation - Impairment of the function of a gene caused by mutation.

missense mutation - A mutation that changes a codon so that it codes for a different amino acid.

nonsense mutation - A mutation in which one of the three terminator codons in the mRNA (UAG, amber; UAA, ochre; UGA, umber or opal), used to signal the end of a polypeptide, appears in the middle of a genetic message, causes premature termination of transcription, and releases incomplete, generally nonfunctional polypeptides from the ribosome.